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The study, published in the PLoS Genetics journal, was produced with colleagues from Cambridge University and other institutions in Australia.

Researchers demonstrated that the gene produces a protein which interacts with other molecules known as intraflagellar transport proteins, the vehicles responsible for carrying genetic information along the length of the sperm's tail.

Jennifer Lo, a PhD student who was lead author of the paper, said: "Intraflagellar transport proteins are like a train. Our data suggests that the reloading of the train is defective if RABL2 dysfunctions.

"The train is still running in sperm tails with dysfunctional RABL2, but it contains fewer passengers. The end result is that sperm formation and motility are abnormal."

Because mutations in the gene decrease sperm count and hamper their swimming ability scientists hope a contraceptive pill could be developed which would lower levels of the protein it produces.

But because the protein is found at lower concentrations in other parts of the body, including the brain, kidney and liver, any future drug would have to specifically affect the testes.

Prof O'Bryan said: "Many of the basic processes of sperm development occur at lower levels in other organs of the body.

"As such, the presentation of a man for infertility treatment offers the opportunity not only to give him the children he desires but also to mitigate future disease."